1. Field of the Invention
This invention relates generally to the field of semiconductor processing, and, more particularly, to a method for reducing junction capacitance using a halo implant photomask.
2. Description of the Related Art
Semiconductor devices, such as transistors, are formed through a series of steps. First a gate is formed over a portion of a substrate. Implants are then conducted to form source/drain (S/D) regions of the transistor. In an N type transistor, N type dopants are implanted in a P type substrate. In a P type transistor, an N type well is typically formed in a portion of the substrate, and the gate is formed over a portion of the N type well. P type dopants are then implanted to form the S/D regions.
Typically, several implantation steps are used to form the transistor. In the following discussion, fabrication of an N type transistor is described. First, a lightly doped drain (LDD) implant is performed using an N type dopant, such as Arsenic. Next, a halo implant is performed using a P type dopant, such as Boron. The halo implant is used to reduce short channel effects associated with the transistor. Short channel effects cause the threshold voltage of the transistor to decrease as the geometry shrinks. Typically, at least a portion of the halo implant is performed at an angle so that some of the dopant is implanted beneath the gate. Following the halo implant, spacers are formed on the gate, and a S/D implant is performed with an N type dopant, such as Phosphorous.
One disadvantage of using a halo implant to reduce the short channel effects is that the presence of the P type halo dopant in the N type S/D regions increases the junction capacitance of the transistor. Increased junction capacitance results in a less efficient transistor.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.